What the product is and who it suits

Fox ESS T20-G3 is a 20kW three-phase transformerless string inverter in the Fox T Series (G3) range. It is intended for grid-connected solar PV systems where a standard domestic single-phase inverter is no longer appropriate and where the site has a genuine three-phase supply. In practical terms, that makes the T20-G3 a good fit for larger houses, mixed domestic and workshop premises, agricultural buildings, office units and small commercial rooftops where array size and expected generation sit well above the level of lower-output three-phase units.

The main reason this exact variant matters is balance. The T20-G3 sits above the T15-G3 and below the T25-G3, so it fills the middle ground for buyers who need a real 20kW AC output but do not want to over-specify the next size up. For many installations, that translates into a neater fit between array design, site export position and budget. On the LAMPS site it also sits logically alongside the wider three-phase solar inverter category and the broader Fox ESS range.

Fox lists the T20-G3 with 20,000W rated AC output and 30,000W maximum PV input power. That combination matters because inverter buying is not only about the headline AC number. The DC side allowance determines how much flexibility a designer has when selecting module count, string length and sensible oversizing. A 30kW maximum PV input gives the T20-G3 enough scope for larger arrays without automatically pushing the project into the next inverter size.

Key features and practical benefits

The core operating figures are strong for this class. Fox states a 140V start-up voltage, 140 to 1000V MPPT operating range, 1100V maximum input voltage, two independent MPPT trackers, 2+2 strings per MPPT, 28A maximum input current and 36.4A maximum short-circuit current. Maximum efficiency is listed as 98.6%, European efficiency as 97.8% and MPPT efficiency as 99.8%.

Those numbers matter in practice because they tell you how flexible the inverter will be on real roofs. A low 140V start-up voltage helps the unit wake earlier in the day. A wide MPPT operating window gives designers more freedom on string voltage. Two independent trackers allow the array to be split across different roof pitches or orientations without forcing everything onto one tracking point. Four total string inputs, arranged as 2+2 across the two MPPTs, are useful on larger systems where the DC layout is more complex than a simple two-string domestic array.

For buyers and installers, the T20-G3 is therefore not just a larger output number. It is a unit built for bigger three-phase array design. It can support sensible DC oversizing within manufacturer limits, deal with more demanding roof layouts and provide a better match for buildings where energy use or export capacity sits above the mid-range.

• 20,000W rated AC output with 22,000VA maximum apparent power
• 30,000W maximum PV input power for larger array design headroom
• Two MPPTs with 2+2 strings per MPPT for more flexible string layout
• 140 to 1000V MPPT range with 140V start-up voltage
• 98.6% maximum efficiency and 97.8% European efficiency

Technical detail that matters in practice

Fox lists the T20-G3 with rated output current of 30.3A and maximum output current of 31.9A. Power factor is adjustable from 0.8 leading to 0.8 lagging. Total harmonic distortion is below 3%. Rated grid arrangements are listed as 3/N/PE 220/380V, 230/400V and 240/415V at 50/60Hz. Those details are important on projects where the electrical design and commissioning conversation goes beyond simple domestic self-consumption. A three-phase inverter at this level has to fit the site supply properly, not just the array size.

Size and installation handling also matter. Fox lists the inverter at 370 × 480 × 183.5mm and 20kg. That keeps the product in a recognisably compact wall-mounted class despite the 20kW output. It is still a serious three-phase inverter, but it is not a bulky floor-standing commercial chassis. For installers, that usually means more freedom when selecting plant-room or external wall positions.

Cooling method is listed as fan cooling, with noise below 55dB. That is worth understanding clearly because some lower-output units in the wider market use natural convection. The T20-G3 uses active cooling to support the higher power level. In most service areas or external positions that is a reasonable trade-off, but it remains a practical siting point rather than a hidden line in the datasheet.

Fox also lists operating temperature from -25°C to 60°C, humidity from 0 to 100% with no condensation, maximum operating altitude of 3000m and night self-consumption below 3W. Those figures support year-round outdoor use where the installation instructions are followed and the location is sensible.

Installation, monitoring and control

The T20-G3 carries an IP65 enclosure rating, so it is suitable for outdoor installation as well as indoor plant-room use. That is helpful on commercial and mixed-use sites where internal wall space is limited or where the shortest cable routes sit on an external elevation. Buyers planning a full PV system normally pair an inverter like this with suitable solar panels and proven solar mounting systems.

Monitoring and control are stronger than the basic model name suggests. Fox lists optional WiFi and 4G monitoring modules, along with RS485, meter, DRM and emergency stop communication interfaces. The display options are given as LCD, touch key, app and website. In practice that means the T20-G3 can be built into projects where the owner or installer wants remote visibility rather than a simple fit-and-forget approach.

Export control is another important point. Fox states that the T-G3 range includes integrated export limitation functionality when a power meter is installed. The manual also makes clear that the power meter must be installed on the grid side to use that function. That matters on sites with export restrictions or where self-consumption strategy is part of the specification. For related equipment, buyers often review the wider optimisers and meters category alongside the inverter itself.

Protection, standards and warranty

Fox lists a strong protection package for the T20-G3, including insulation monitoring, residual current monitoring, DC reverse polarity protection, anti-islanding protection, AC short-circuit protection, AC overcurrent protection, AC overvoltage protection and Type II surge protection on both the DC and AC sides. DC switch, PV string current monitoring and AFCI are listed as optional functions. These points are commercially important because they shape how the inverter behaves in commissioning, fault management and long-term operation.

Safety standard coverage is listed as IEC 62109-1 and IEC 62109-2. EMC standards are listed as EN 61000-6-1, EN 61000-6-2, EN 61000-6-3 and EN 61000-6-4. Grid regulation listings include EN 50549-1 among other regional standards. That is stronger and more useful than vague marketing language because it tells installers what formal technical framework the unit has been built against.

Warranty should also be read carefully. Under the current UK and Ireland Fox inverter warranty policy, the standard warranty is sixty months from the date of installation, capped at sixty-five months from the date of manufacture, whichever comes first. For T Series products, Fox also states that a further sixty months can be added where the product is registered within the stated timeframe and registered to Fox Cloud using a Fox datalogger for remote monitoring. That extended-cover route is a practical buying point, but only where the registration conditions are actually met.

Why this variant may be the better fit

The T20-G3 is the model to choose when a 15kW three-phase inverter is too small but a 25kW unit would be unnecessary. That sounds simple, but it has real implications in specification. The T20-G3 gives 20kW AC output and 30kW maximum PV input, so it can support larger roof areas and more ambitious DC sizing than the T15-G3 while avoiding the extra step up in capacity and cost that can come with the T25-G3.

That middle-ground position is exactly why the model exists. For a building with larger daytime load, a bigger three-phase roof and some export-control considerations, 20kW can be the most natural fit. Buyers who are still sizing the project can compare it with the Fox ESS T15-G3 below it and the Fox ESS T25-G3 above it in the same family.

Frequently asked questions

Loading delivery information...